Mammary Analogue Secretory Carcinoma (MASC)

Mammary Analogue Secretory Carcinoma (MASC)

Mammary Analogue Secretory Carcinoma (MASC) of the salivary gland was first described by Skálová in 2010. A chromosome translocation was found to be identical to the t(12;15) (p13;q25) of secretory carcinoma of the breast. This fusion is within the gene.
The fusion gene product contains the N-terminus of the transcription faction TEL that is responsible for dimerization/polymerization of ETV6. The C-terminus of the protein product of the gene fusion contains the C-terminus of the receptor tyrosine kinase Tropomyosin receptor kinase C. It should be noted that the fusion protein lacks regulation by growth factors. Since it's discovery, much of the literature concerning MASC has addressed the challenge of differentiating it from similar appearing cancers such as acinic cell carcinoma (AciCC), low-grade cribriform cystadenocarcinoma (LGCCC), and adenocarcinoma not otherwise specified (AcNOS). Means of identifying and differentiating MASC rely on histology, protein markers, and genetic markers.
**Picture courtesy: Alena and Biopticka Laborator

Kensuke Suzuki and coworkers of the Kansai Medical University Hospital (Hirakata, Japan) reported a case of lymph node MASC (mammary analog of secretory carcinoma treatment) with no discernible primary site of origin. The patient was a 74 year old male presenting with a painless mass in his left neck. This publication was a nice education on some of the techniques used to assess head and neck cancers. It also highlights the need to test cervical lymph nodes for MASC even when the salivary glands appear to be normal.

Figure 1. Two images of lymph nodes from Human Anatomy ChartsA. lymph nodes are reservoirs of immune cells B. Lymph nodes of the head and neck. Note the lymph nodes associated with salivary glands.

It is interesting to note that lymph nodes are reservoirs of cells of hematopoetic origin and that the ETV6-NTRK3 rearrangement has been observed in hematopoetic malignancies.

Sonography is a common way of viewing cancers of the head and neck (Figures 2A-B, Figure 1A-B in Suzuki 2017). Suzuki and coworkers claimed that the lymph node tumor was hypoechoic, meaning that it reflects sound waves less than surrounding tissue. Blood, fluids, and fat tend to be hypoechoic whereas air is hyperechoic. The computed tomography image (Fig 2C) shows a lesion (arrows) in the left upper neck. Contact is made with the carotid bifurcation and the jugular vein. CT images are computer generated from multiple X-ray images.

The lymphatic system is shown in Figure 3A. Positron emission tomography/computed tomography (PET-CT) creates images of high glucose utilization based on the glucose analog (18F) fluorodeoxyglucose. This radioactive analog emits a positron, the basis of positron emission tomography (PET). FDG avidity was seen in the left-sided neck at a level II lymph node, the size of which was 21 × 16 mm. Compare this avidity with that of the patient’s brain and kidneys (Figure 3B). Also note the lack of FDG avidity in the region of the patient’s salivary glands and (male) breast tissue. No other lymph nodes seem to be “lighting up” with FDG.

Figure 3. The lymphatic blood flow with lymph nodes in the neck in red. B. PET-CT scan of the patient, Fig 1d in Suzuki 2017.

Further details of the tumor were revealed by surgical resection.

The tumor had invaded the internal jugular vein and the superior thyroid artery. These vessels were sacrificed.

The parotid and submandibular glands were not involved.

Poorly differentiated adenocarcinoma was suspected.
The resected tumor had the yellow/white coloration seen in MASC.

Even though salivary glands were not involved in any way that could be seen by non invasive imaging, immunohistochemistry and ETV6 break apart FISH (not shown) were performed. The protein markers were DOG1, GATA 3 and S100.

While the ETV6 break apart FISH assay has a long history in identifying MASC, it is not recommended for oncologists looking for a precision medicine for their patient. A more reliable test is the Trailblaze Pharos assay that uses (1) a pan-receptor tyrosine kinase IHC (2) pan Trk (and more) IHC, and (3) next generation sequencing of transcripts to identify the TEL-TrkC fusion protein transcript. Follow this link to learn more about a Trk treatment.

If this patient had been proven to carry the ETV6-NTRK3 gene rearrangement or another NTRK, ROS1, or ALK gene rearrangement he may have been eligible for a salivary gland cancer trial . It should be noted that the authors reported that once the lymph node was resected, the tumor failed to return after nine months.

Since this blog was first published, mammary analog of secretory carcinoma (MASC) has come to be known as simply secretory carcinoma. The following is an account of back tracking gene transcription alterations in a secretory carcinoma of the breast model to the AP-1 transcription factor.

This work was performed by Li and coworkers in Stuart Okin’s lab when ETV6-NTRK3 was linked to secretory carcinoma. These authors produced a murine model of human sporadic breast cancer using a Cre-Lox recombination to generate the ETV6-NTRK3 translocation.

Creation of a murine model of secretory breast cancer:

The Cre-Lox system was used to knock-in the protein tyrosine kinase (PTK) domain of human NTRK3 to the 5′ end of exon 6 of the mouse ETV6 gene. Li and coworkers used a model of Wagner et al., (1997) that ties the Cre-Lox recombination to the activation of the Wap promoter. In maturing and mature nulliparous (never given birth) female mice, wap+ cells are present only transiently as a minor subset at estrus. Wap expression is greatly elevated in differentiating mammary epithelial cells (MECs) during late pregnancy and lactation, and then turned down following involution, when the pups are weaned. In this way, Li and coworkers were able to time the ETV6-NTRK3 recombination to days 10-18 of pregnancy when alveolar proliferation and differentiation occurs.

The Leeman-McNeill 2014 study we are reviewing was a follow up of a previous 2013 study in 62 papillary thyroid carcinoma (PTC) patients who received 0.0008-8.6 Gy of 131I to the thryoid during the 1986 Chernobyl accident. Almost two thirds of the tumors from these individual showed RET and PAX8/PPAR chromosomal breaks as well as some RAF and BRAF point mutations (Leeman-McNeill 2013). These markers, however, failed to explain almost 40% of the tumors.

Why is it that MASC tumors retain the lobular growth pattern in spite of being driven by a neuronal protein kinase? Lobular growth in salivary glands is influenced by mechanical forces and FGF10. The same three signal transduction pathways activated by neurotrophins binding to Trk kinases are activated in salivary gland lobular growth. This observation is posted for consideration.

Control of lobular growth:

What controls lobular growth pattern in salivary glands and other similar tissues in which MASC tumors arise? Jeff Hsu and Kenneth Yamada of the Laboratory of Cell and Developmental Biology at the NIH in Bethesda addressed this matter in a 2010 review. The quick answer is the same pathways activated by the Trk kinases: PI3K, PLCγ, and MAPK.

Vimentin is a ubiquitous intermediate filament protein often expressed in very large amounts in tissues requiring structural integrity. In spite of this, the VIM gene is under developmental control. Vimentin is often used as a biomarker of developmental transitions. Vimentin has numerous sits of post translational modification and regulation. Vimentin may also do some interesting things in the cancer process.

Keratin isoforms have become popular biomarkers, in particular a subtype of epithelium from which MASC arises. A greater understanding of their function and expression may lead to a greater understanding of what they are reporting as biomarkers. The genes coding for the neutral/basic monomers of keratin are clustered in the q13.13 region of the long arm of chromosome 12. Genes coding for the acidic monomers are clustered in the q21.2 region in the long arm of chromosome 17. Keratin isoform pairs distribute differently from one tissue to another. Note that the KRT7 and KRT19 pair have been used to define MASC. Each monomer has three domains.

Described on gastrointestinal stromal tumors (DOG1), DOG1 is better known as the calcium activated chloride channel anoctamin 1 (Ano1). Ano 1, coded for by the ANO1 gene, is a voltage-sensitive calcium-activated chloride channel expressed in smooth muscle and epithelial cells. It is highly expressed in human interstitial cells of Cajal (ICC) throughout the gastrointestinal tract.

How could mammaglobin relate to MASC and the ETV6-NTRK3 rearrangement that drives MASC? In 2016 Picot and coworkers in the Robichaud Laboratory published some excellent work on what a favorite cancer biomarker, mammablobin, might actually be doing to promote carcinogenesis. These authors viewed metastasis as a two part processes.

MASC: A disease of out of control feed forward signaling loops (hypothesis)

Feed forward loops are comparatively fewer in number in biology. One well known example is partition Figure 1A. The more the fetus grows, the more pressure it puts on the cervix, the lower portion of the uterus. This stretching sends impulses to the brain that cause the release of the hormone oxytocin. Oxytocin causes the uterus to contract around the baby putting even more pressure on the cervix. When the feed forward reaches its end point, the baby is born. When feed forward loops in cancer reach their end point, the patient dies. The following is an exploration of potential feed forwards loops in MASC.

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